1. Field of the Invention
The present invention relates to a method for manufacturing a discharge head, and a discharge head, and more particularly, to a method for manufacturing a discharge head having a thin film laminate structure, and a structure for same.
2. Description of the Related Art
In recent years, inkjet printers have come to be used widely as data output apparatuses for outputting images, documents, or the like. By driving recording elements, such as nozzles, provided in a recording head in accordance with data, an inkjet printer is able to form data onto a recording medium, such as recording paper, by means of ink discharged from the nozzles.
In an inkjet printer, a desired image is formed on a recording medium by causing a recording head having a plurality of nozzles and a recording medium to move relative to each other, while causing ink droplets to be discharged from the nozzles.
The print quality of the image output by the inkjet recording apparatus depends largely on the performance of the print head mounted in the apparatus. In other words, in order to improve print quality in the output image, it is necessary to improve the characteristics of the print head.
A print head installed in an inkjet recording apparatus may be a full line type print head which has a nozzle row of a length corresponding to the full width of the recording medium, or a serial (shuttle scanning) type of print head which has a nozzle row of a length shorter than the width of the recording medium and which forms a line in the breadthways direction of the recording medium by scanning in this breadthways direction. In a full line type print head, it is possible to perform single-pass printing whereby an image is formed over the whole print region of the recording medium, by scanning the print head once of the recording medium. Therefore, high-speed printing is possible, in comparison with a serial type head.
In order to improve image quality, it is necessary to form very fine dots at high density on the recording medium. This means positioning nozzles having very fine hole diameter at high density in the print head, and ultra-fine processing technology having good processing accuracy is used to form the nozzles and pressure chambers (ink chambers) in the print head.
However, in a long print head, such as a full line print head as described above, warping of the head structure is liable to occur. In particular, warping is more liable to occur in the lengthwise direction, compared to the breadthways direction, and if warping occurs in a print head, then this has a significant effect on printing performance.
For example, if the print head suffers warp in the lengthwise direction, then the clearance between the surface of the print head on which the nozzles are formed (the surface of the print head opposing the recording medium) and the recording medium may vary between the central region of the head and the respective end regions of the head, and a large error may arise in the landing positions of the ink droplets ejected from the nozzles in the vicinity of the end regions of the head. Moreover, if one print head is provided for each respective color, in order to achieve color image printing, then any error in landing positions between the respective heads will cause color irregularities.
In this way, warping of the print head causes image blurring and color irregularities, and hence has a major impact on the quality of the images output by the inkjet printer.
In general, a print head installed in an inkjet printer, or the like, has a laminated structure in which a plurality of thin film (thin plate) members are layered together. If there is warping of the members forming the respective layers, then problems arise, such as bonding faults between the layers, and misalignment of connecting holes, openings, and the like, between layers. Therefore, it may become impossible to achieve the desired printing characteristics. Furthermore, in a laminated structure in which a plurality of thin film members are layered together, warping is liable to occur when the structure returns to normal temperature after heat treatment steps, due to differences in the thermal expansivity of the respective layers.
In order to resolve problems of this kind, processing methods and materials suited to these methods are selected for the members forming each layer, according to the processing accuracy required. On the other hand, printing characteristics are maintained in the print head by selecting materials that are not liable to warping (namely, materials having a low coefficient of thermal expansion), in order to prevent warping during heat treatment, and by devising the manufacturing process and the head structure in such a manner that even if the constituent members of the print head do warp, the warping is mutually cancelled out between the respective layers, and hence warping is cancelled out in the laminated structure as a whole.
In the liquid discharge head and method for manufacturing same described in Japanese Patent Application Publication No. 2003-136714, the diaphragm is made of a metallic oxide material, and the walls of the pressure chambers are made of a corrosion-resistant metal, thereby increasing the corrosion resistance of the pressure chambers.
Furthermore, in the discharge head and method for manufacturing same described in Japanese Patent Application Publication No. 2003-136715, the diaphragm is made of a piezoelectric material and the pressure chamber walls are made of a corrosion-resistant metal, in such a manner that the diaphragm is also used as a piezoelectric body.
However, in order to achieve high-precision ultra-fine processing, it is necessary to use a material suited to the processing method in each layer. This means using different materials in each of the layers constituting the laminated structure, and if these materials have different coefficients of thermal expansion, then warping will occur after heat treatment. Furthermore, materials that are not liable to warping are difficult to process, or require special processing technologies, and the difficulty of post-processing and the number of processing steps may increase.
In the discharge head and the method for manufacturing same described in Japanese Patent Application Publication Nos. 2003-136714 and 2003-136715, a corrosion-resistant metal is used as the material for the pressure chambers, and wet etching is used-to form the pressure chambers. For example, if stainless steel is used as the material for the pressure chambers, then it is difficult to form very fine shapes without curved edges or tapering, by controlling the etching liquid during wet etching. Moreover, taking account of the warping caused by heat generated when forming the piezoelectric film on the substrate (diaphragm plate) by aerosol deposition, it is necessary to form the substrate to a large thickness. This is disadvantageous in terms of processing accuracy when processing shapes of high aspect ratio in order to form pressure chambers in the substrate by etching.